Light source device for an image forming apparatus

ABSTRACT

A light source device for use in an image forming apparatus and using a semiconductor laser is disclosed. The device needs a minimum of constituent parts and frees the individual part from dislocation in the event of assembly. A collimator lens included in the device is fixed in place by photo-curable adhesive. The device is low cost and highly accurate.

BACKGROUND OF THE INVENTION

The present invention relates to a light source device for use in animage forming apparatus and using a semiconductor laser.

A digital copier, laser printer, facsimile apparatus or similar imageforming apparatus extensively used today includes a light source devicehaving a semiconductor laser and a collimator lens. Opticalcharacteristics required of the light source device include thedirectivity of laser light (optical axis characteristic) and theparallelism of a beam (collimation characteristic). To meet theserequirements, it is a common practice to adjust the relative position ofthe emission point of the laser and the collimator lens in thedirections of three axes (x, y and z). The positional accuracy isseverely restricted to below the order of microns. Therefore, the deviceusing the laser and collimator lens must be capable of being adjusted inthe three axis directions and then fixed at its adjusted position.

When the collimator lens is fixed in place by adhesive, the adhesivecontracts in the event of setting. It is therefore necessary to reducethe influence of the contraction on the optical characteristics as faras possible. Particularly, high accuracy is required of the device inthe direction z (optical axis direction), so that the contraction shouldpreferably be prevented from occurring in the direction z. For thispurpose, the adhesive layer should preferably extend substantiallyparallel to the optical axis (axis z), Also, the contraction shouldpreferably be limited to one of the directions x and y in order tofacilitate adjustment even in such a direction.

Light source devices each having a semiconductor laser and a collimatorlens are taught in, e.g., Japanese Patent Laid-Open Publication Nos.5-88061, 5-136952, and 5-273483.

However, the conventional devices of the type described have someproblems yet to be solved, as follows:

(1) Each device needs a number of constituent parts which increase thecost.

(2) The constituent parts are dislocated in the directions x, y and z inthe event of assembly, so that the directivity (optical axischaracteristic) of the laser is deteriorated.

(3) Use cannot be made of ultraviolet light curable adhesive for fixingthe collimator lens in place. This kind of adhesive can set in a shortperiod of time in a desired manner and is highly reliable.

The conventional devices have other problems which will be described, inaddition to the above problems.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aninexpensive and highly accurate light source device needing a minimumnumber of constituent parts, protecting the individual part fromdislocation during assembly, and allowing a collimator lens to be fixedin place by photo-curable adhesive.

In accordance with the present invention, a light source device has aflat base member having a through bore. A semiconductor laser foremitting laser light is mounted on the rear of the base member andfitted in the through bore. A lens is mounted on the front of the basemember at the front of the through bore and coaxial with the opticalaxis of the semiconductor laser. A lens support member is positioned atthe front of the through bore coaxially with the optical axis of thesemiconductor laser. The lens support member has a n arcuate section anda diameter slightly greater than the outside diameter of the lens. Thelens is affixed to the lens support member by photo-curable adhesive.

Also, in accordance with the present invention, a light source devicehas a base member having a through bore substantially at the centerthereof. A semiconductor laser is fitted in the through bore foremitting laser light. A lens is mounted on the surface of the basemember. A lens support member supports the lens positioned in thedirections of three axes with adhesive filling a clearance between thelens and the surface of the base member.

Further, in accordance with the present invention, a light source devicehas a semiconductor laser for emitting laser light, a first supportmember supporting the semiconductor laser, a lens positioned coaxiallywith the optical axis of the semiconductor laser, and a second supportmember supporting the lens. The first support member has a firstreference surface perpendicular to the optical axis of the semiconductorlaser. The second support member has a second reference surface parallelto the optical axis of the semiconductor laser.

Moreover, in accordance with the present invention, a light sourcedevice has a semiconductor laser for emitting laser light, a firstsupport member supporting the semiconductor laser, a lens positionedcoaxially with the optical axis of the semiconductor laser, a secondsupport member supporting the lens, an aperture forming member having anaperture for shaping the laser light issuing from the semiconductorlaser, and a third support member supporting the aperture forming memberon the second support member from below the second support member. Thefirst support member is positioned perpendicularly to the optical axiswhile the second support member is located in front of the first supportmember.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptiontaken with the accompanying drawings in which:

FIG. 1 is a vertical section showing a conventional light source device;

FIG. 2 is an external perspective view showing another conventionallight source device;

FIG. 3 is a vertical section showing a first embodiment of the lightsource device in accordance with the present invention;

FIG. 4 is an exploded perspective view of the first embodiment;

FIG. 5 is a front view of a collimator lens and a lens support portionalso included in the first embodiment;

FIG. 6 is a section of the collimator lens and lens support portionshown in FIG, 5;

FIGS. 7-13 are sections each showing a particular configuration ofnon-adhesion portions included in the lens support portion;

FIG. 14 is a vertical section showing a second embodiment of the presentinvention;

FIG. 15 is a vertical section showing a third embodiment of the presentinvention;

FIG. 16 is a section along line XVI--XVI of FIG. 15;

FIG. 17 is a vertical section showing a fourth embodiment of the presentinvention; and

FIG. 18 is a plan view of the fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To better understand the present invention, a brief reference will bemade to a conventional light source device of the type having asemiconductor laser and a collimator lens, shown in FIG. 1. This type oflight source device is taught in, e.g. previously mentioned JapanesePatent Laid-Open Publication No. 5-88061.

As shown in FIG. 1, the light source device has a base or support member101 formed with a stepped through bore 102. A semiconductor laser 103for emitting laser light is press fitted in the bore 102. For the base101, use is made of resin for low cost or of aluminum or similar metalfor precision, as needed. A flange 105 is fastened to the base 101 bytwo screws 104. A bore 106 is formed in the flange 105 in alignment withthe bore 102 of the base 101. The bore 106 merges into an inlet portion106a located at the left-hand side of the bore 106, as viewed in FIG. 1.The inlet portion 106a is about 1 mm greater in diameter than the bore106. A hollow cylindrical lens holder 107 is received in the bore 106and spaced from the wall of the bore 106 by a clearance of about 0.01 mmto 0.03 mm. A collimator lens 108 is fixed in place in the lens holder107 in order to transform the laser light to a parallel beam.

A printed circuit board 109 is formed with positioning holes 110. Guidepins 111 protruding from the end of the base 101 are respectivelyreceived in the holes 110. The tips of the guide pins 111 are deformedby heat, as indicated by dash-and-dots lines in FIG. 1. As a result, thebase 101 and circuit board 109 are affixed together. Leads 112 extendingout from the laser 103 are passed through lead holes formed in thecircuit board 109 and soldered to a conductive wiring pattern formed onthe rear of the circuit board 109. If the base 101 is made of metal,then the guide pins 111 will be replaced with threaded holes formed inthe end of the base 101. In this case, the base 101 and circuit board109 will be fastened to each other by screws.

The flange 105 is accurately positioned such that the emission point ofthe laser 103 aligns with the optical axis of the collimator lens 108.In this condition, the flange 105 is fastened to the base 101 by thescrews 104. The flange 105 has a notch 113 communicated to the inletportion 106a. After the lens holder 107 has been positioned in thedirection z such that the emission point of the laser 103 coincides withthe focus of the collimator lens 108, adhesive is introduced into theflange 105 via the notch 113. As a result, the lens holder 107 isaffixed to the flange 105 by the adhesive.

An aperture forming member 114 plays the role of a shield cap forseparating the central parallel part of the beam transmitted through thecollimator lens 108, i.e., for thereby shaping the beam. The apertureforming member 114 has an aperture 114a for shaping the beam, and aprojection 114b.

The member 114 is affixed to the flange 105 with its projection 114bmating with the notch 113.

When the above light source device is mounted to the body of a copier,laser printer or similar image forming apparatus, a flat surface 105aincluded in the flange 105 and perpendicular to the optical axis is usedas a reference surface. The surface 105a is also used as a reference forthe adjustment of optical characteristics.

FIG. 2 shows another conventional light source device taught in, e.g.,previously mentioned Japanese Patent Laid-Open Publication No. 5-136952or 5-273483. As shown, the light source device has a barrel 121 holdinga collimator lens 120. The barrel 121 is received in a holder 122. Asemiconductor laser 123 is mounted on a printed circuit board 124 whichis in turn at-fixed to a base 125. The base 125 is retained by pawl-likeprojections 122d extending from the holder 122. Adhesive is introducedinto grooves 122a and 122b and a hole 122c formed in the holder 122. Asa result, the base 125 and barrel 121 are affixed to the holder 122 bythe adhesive.

The conventional devices described above, particularly the device shownin FIG. 1, have the following problems left unsolved.

(1) The adjustment in directions x and y (optical characteristic) andthe adjustment in the direction z (collimation characteristic or focaldirection) are each effected by a respective structure. This increasesthe number of structural parts and therefore the production cost of thedevice.

(2) The outside diameter of the lens holder 107 and the inside diameterof the bore 106 of the flange 105 must have strict accuracy. Thisincreases the production cost of the lens holder 107 and flange 105.

(3) After the adjustment in the directions x and y, the flange 105 isfastened to the base 101 by the screws 104.

Therefore, when the screws 104 are driven into the flange 105 and base101, screw seats provided on the end of the base 101 and the flange 105bite into each other. This is apt to bring about dislocation in thedirections x and y, thereby lowering the accuracy of the directivity(optical axis characteristic) of the laser.

(4) Because the laser light issuing from the laser 103 has a certainspread, it is not always entirely incident on the collimator lens 108.Lasers in general are restricted by legal safety standards. It ispreferable that a laser beam issuing from a laser be prevented fromleaking in directions other than the direction of an optical axis. Thisis true not only when the laser is in use but also when adjustment iseffected on the production line. Therefore, the flange 105 and base 101must be made of materials which intercept the laser beam.

(5) The adhesive for affixing the lens holder 107 should preferably beultraviolet light curable. This kind of adhesive hardens rapidly in adesired manner and is therefore desirable from the production time andreliability standpoint. However, because the base 101 and flange 105 aremade of materials opaque to ultraviolet rays, ultraviolet rays cannotuniformly illuminate the entire adhesive even even if radiated via theclearance through which the adhesive has been introduced. This resultsin irregular hardening and unhardened portions. Consequently, strainsascribable to contraction caused by hardening act unevenly on theassembly, resulting in the dislocation of the lens holder 107 and thecracks of the structural parts. Materials opaque to the laser light,which may be infrared rays or red light, issuing from the laser 103 are,of course, opaque to ultraviolet rays having a longer wavelength thanthe laser light. Therefore, to transmit only ultraviolet rays, there isneeded a special filter or a special coating on the flange 105,increasing the cost to a noticeable degree. This obstructs the use ofthe ultraviolet light curable adhesive.

(6) Because the adhesive exists on the entire periphery of the lensholder 107, i.e., in both the direction x and the direction y, thedirection of the contraction of the adhesive is not limited to thedirection x or y. As a result, the positional accuracy is irregular inthe directions z and y. To guarantee the positional accuracy after theadhesion, it is necessary to provide the initial position with an offsettaking account of a certain degree of contraction. However, because thedirection of contraction is not fixed, it is difficult to implement theoffset. This sometimes lowers the accuracy of the directivity of thelaser (optical axis characteristic).

(7) Because the adhesive is introduced via the notch 113, it is apt topartly solidify or contract or to flow in an irregular manner. As aresult, a strain occurs in the optical axis direction (direction z) andrenders positional accuracy irregular.

(8) The light source device is disposed in the body of an image formingapparatus. Because the temperature in the apparatus body is usuallyhigh, the device is also subjected to high temperature during the courseof operation. This, coupled with the fact that the laser 103 itselfgenerates heat, elevates the temperature of the device. The prerequisiteis therefore that the relative position of the laser 103 and lens 108adjusted in the directions x, y and z be surely held in a certain rangeeven at high temperatures. Particularly, the displacement in thedirection of optical axis (direction z) is severely restricted. Underthese circumstances, if the base 101 is formed of ordinary resin to meetthe cost reduction requirement, then its heat radiation ability islowered and deteriorates the characteristic of the entire assembly in ahigh temperature environment. Furthermore, the portions of the base 101and flange 105 fastened by the screws 104 are not strong, so that therelative position of the laser 103 and lens 108 is apt to vary due tothe fastening torque. Particularly, when a thermal stress is applied tothe assembly, the base 101, flange 105 and screws 104 each expands to aparticular degree due to the respective coefficient of thermalexpansion. As a result, after the application of the thermal stress, thefastening stress and therefore the relative position of the laser 103and lens 108, i.e., the collimation characteristic is apt to vary. Inlight of this, the base 101, flange 105 and screws 104 may all be formedof the same material having a single coefficient of linear expansion.However, if the base 101 and flange 105 are formed of resin, the screws104 must also be formed of the same resin, resulting in an increase incost.

(9) The laser 103 for the light source device is provided with variouskinds of configurations, depending on the configuration of an imageforming apparatus, among others.

For example, a case surrounding the laser 103 may be used as a powersource terminal (e.g. 5V). In this case, however, the laser 103 does notemit light when the case surrounding it is brought to the ground level.It is therefore necessary to isolate the case from the ground level notonly when the device is assembled but also when it is mounted to theapparatus body. If the base 101 and flange 105 are formed of metalradiating heat efficiently, then the device must include a portion forinsulating the case of the laser 103 because the entire device isconductive. In addition, the base 101, flange 105 and screws 104 must beformed of the same metal at the sacrifice of cost, as stated in theabove item (8).

(10) To adjust the focus of the collimator lens 108 (direction z), theparallelism (collimation characteristic) of the laser beam shaped by theaperture 114a is detected. Generally, because the laser beam coming outof the aperture 114a tends to spread due to diffraction, the parallelismof the beam differs from the case including the aperture 114a to thecase lacking it. Further, the degree of parallelism depends on thecharacteristic of the individual laser 103. The parallelism of the laserbeam necessary for the light source device is the characteristic of thebeam coming out of the aperture 114a; that is, the light transmittedthrough the peripheral portion of the lens 108 is not necessary. Theperipheral portion of the lens 108 is noticeably affected by aberrationand greatly differs from one lens to another lens. Therefore, even whenthe parallelism of the entire beam is detected and satisfies therequired accuracy, it is sometimes unsatisfactory when it comes to thepart of the beam around the center. It follows that ideally the focus ofthe lens 108 should be adjusted after the aperture forming member 114has been mounted. However, because the aperture forming member 114covers the lens 108, the lens 108 cannot be adjusted after the mountingof the aperture 114a. As a result, the parallelism of the laser beamvaries after the mounting of the aperture 114a.

(11) The light source device is fastened to the apparatus body by screwswith the surface 105a of the flange 105 serving as a reference. Screwsare driven into the reference surface 105a from above the apparatus bodyor from one side of the apparatus body, depending on the configurationof the apparatus body. However, the device can be fastened only from theside of the apparatus body because the reference surface 105a isperpendicular to tee optical axis of the laser beam. When the flange 105must be fastened from above the apparatus body, an intermediary mountingmember is required. This not only increases the cost but also lowers theaccuracy of optical axis characteristic due to the intermediary member.As a result, the device lacks in general-purpose applicability. This isalso true with the light source device shown in FIG, 2 because it isconfigured to be mounted from above the apparatus body.

(12) The laser 103 is easily deteriorated or damaged by staticelectricity or similar electrical noise. Ideally therefore, the deviceshould be assembled and adjusted fully automatically so as to beisolated from static electricity issuing from the human body. Theautomatic assembly and adjustment will save labor cost and will improvequality and yield of products. In an automatic machine, the referencesurface for setting workpieces including light source devices shouldadvantageously be horizontal, considering the loading and unloading ofthe workpieces. When the production of the light source device havingthe reference surface 105a perpendicular to the optical axis isautomated, it should preferably be set face down (causing the laser beamto issue downward) in order to facilitate the production. However, sucha configuration requires the adhesive to be introduced into the assemblydownward or sideways after the adjustment of the collimator lens 108.This is not practical, considering the drop of the adhesive. Moreover,the aperture must be mounted to the assembly from below the assemblyafter the injection of the adhesive, complicating the automatic machineor requiring an extra step.

Preferred embodiments of the light source device in accordance with thepresent invention will be described which are free from the problemsdiscussed above.

1st Embodiment

Referring to FIGS. 3-13, a light source device embodying the presentinvention is shown. As shown in FIGS. 3 and 4, the device has a printedcircuit board 1, a semiconductor laser 2, a flat base 3 for holding thelaser 2, a collimator lens 4, and an aperture forming member 5. In theillustrative embodiment, the base 3 is formed of insulating resin havinga coefficient of linear expansion of 2.3×10⁻⁵ /K or below, as measuredin the optical axis direction, and a thermal conductivity of 0.9 W/m-Kor above. This kind of resin surely provides the base 3 with acollimation characteristic and a heat radiation characteristic againstchanges in temperature. For example; use may be made of unsaturatedpolyester resin containing glass fibers and satisfying the aboveconditions. The base 3 is opaque to an infrared laser beam issuing fromthe laser 2 (eg. 780 nm) and light shorter in wavelength than the same.

A stepped through bore 3a is formed throughout substantially the centerof the base 3. The laser 2 is press fitted in the bore 3a from the rearof the base 3. Because unsaturated polyester resin with glass fibers andconstituting the base 3 is insulative, a case surrounding the laser 2and mounted to the base 3 is fully electrically insulated. Thiseliminates the need for special insulation otherwise provided on thecase of the laser 2.

Two spacers 3b protrude from the rear of the base 3, and each is formedwith a threaded bore 3c for affixing the printed circuit board 1. Twothrough holes 1a are formed in the circuit board 1 in alignment with thespacers 3b. Screws 6 are respectively driven into the threaded bores 3cvia the holes 1a, thereby fastening the base 3 and circuit board 1together. If desired, the threaded holes 3c and screws 6 may be replacedwith simple holes and tapping screws, respectively.

Three leads 2a extending out from the laser 2 are respectively passedthrough Lead holes 1b formed in the circuit board 1 and are soldered toa conductive wiring pattern provided on the rear of the circuit board 1.

The collimator lens 4 is directly affixed to the base 3 by adhesive. Forthis purpose, a lens support potion 3d is formed integrally with thebase 3 and coaxially with the optical axis of the laser 2. The leassupport portion 3d is positioned at the front of the bore 3a andprovided with an arcuate section. This portion 3d is slightly greater indiameter (e.g. about 0.3 mm) than the outside diameter of the collimatorlens 4. As shown in FIG. 7, the lens support portion 3d has a length inthe optical axis direction (direction z) great enough to formnon-adhesion portions G1 and G2. Even when adhesive 8 is applied in anexcessive amount, the portions G1 and G2 prevent it from depositing onthe other portions. This will be described specifically later. The arcof the lens support portion 3d is smaller than a semicircle, as seenfrom the front.

As shown in FIG. 5, the arc of the lens support portion 3d as viewed ina section should preferably extend over an angle of about 60 degrees andbe symmetrical in the right-and-left direction.

The collimator lens 4 is formed of a material transparent to ultravioletrays. While the lens 4 may be implemented as a plastic lens or a glasslens, a glass lens is superior to a plastic lens as to opticalcharacteristic. As shown in FIG. 5, in the event of assembly, the lens 4is held by a chuck 7 adjustable in position in the directions x, y andz. Then, the lens 4 is positioned on the lens support portion 3dcoaxially with the laser 2. Subsequently, the ultraviolet light curableadhesive 8 is filled in the clearance between the surface 3e of the lenssupport portion 3d and the outer periphery of the lens 4. Thereafter,the position of the lens 4 is finely adjusted while having its opticalcharacteristic monitored by a testing device, not shown. As soon as thelens 4 is brought to a position where it obtains a desired opticalcharacteristic, the chuck 7 is fixed in place there. Then, as shown inFIGS. 5 and 6, an ultraviolet radiator 9 radiates ultraviolet rays Ltoward the adhesive 8 from above the collimator lens 4. The ultravioletrays L are incident to the adhesive 8 by way of the lens 4 and causes itto set uniformly. As a result, an adhesive layer of uniform thicknessand symmetrical in the right-and-left direction is formed between thesurface 3e of the support portion 3d and the lens 4. The adhesive layerhas a thickness equal to the gap between the surface 3e and the Lens 4(about 0.3 mm). The lens 4 is affixed to the support portion 3d by theadhesive layer while maintaining the desired optical characteristics.

Particularly, the arcuate section of the lens support portion 3d whichextends over about 60 degrees, as shown in FIG. 5, has the followingadvantages. The chuck 7 can support the collimator lens 4 surely andeasily. Because the ultraviolet rays L issuing from the radiator 9 areuniformly incident to the entire surface 3e via the lens 4, the adhesive8 can set evenly over its entire area. Such a uniform and fully setadhesive layer prevents the lens 4 from being displaced due to irregularhardening and unhardened portions.

Further, strains ascribable to contraction of the adhesive 8 occursymmetrically in the direction x (right-and-left direction) andtherefore cancel each other. As a result, a strain occurs only in thedirection y (up-and-down direction). It is therefore possible to providethe initial position of the collimator lens 4 with a slight offset inthe direction y before hardening, taking account of the contraction.This enhances the accuracy in the optical characteristic of the lens 4after fixation.

The base 3 is formed of an insulating material having a particularcoefficient of linear expansion in the axial direction and a particularthermal conductivity, as stated earlier. Despite that the laser 2generates heat, the great thermal conductivity of the base 3 allows thetemperature of the light source device to rise only about 5° C. at mostabove the temperature inside the apparatus body. Moreover, thecoefficient of linear expansion of the base 3 is as small as that ofaluminum. Hence, even if the temperature of the light source devicerises about 5° C., it does not cause the relative position of the laser2 and lens 4 to change noticeably. In addition, the collimationcharacteristic of the lens 4 is held stable against changes intemperature.

As shown in FIGS. 3 and 4, the base 3 additionally has an annularstepped portion 3h at the root of the lens support portion 3d. Thestepped portion 3h has at its end an annular recess 3 k concentric withthe bore 3b and greater in diameter than the collimator lens 4. Therecess 3 k is deep enough to prevent the adhesive 8 from depositing onthe surface of the stepped portion or base wall 3h when the adhesive 8spreads more than the expected degree. Specifically, as shown in FIG. 7,the previously mentioned non-adhesion portion G1 is formed between thesurface of the base wall 3h and the lens 4. Further, the tip of thesupport portion 3d extends forward sufficiently over the lens surface ofthe lens 4, so that even the adhesive 8 spread excessively toward thetip of the support portion 3d will not drop. Specifically, as shown inFIG. 7, the previously mentioned non-adhesion portion G2 is formedbetween the tip of the support portion 3d and the lens 4.

Assume that the adhesive 8 is filled in the gap between the collimatorlens 4 and the support portion 3d in an excessive amount. Then, thenon-adhesion portions G1 and G2 sandwiching the lens 4 prevent theadhesive 8 from depositing and solidifying on the surface of the basewall 3h or from solidifying while dropping from the tip of the supportportion 3d, as shown in FIG. 8. Assume that the above portions G1 and G2are absent. Then, as shown in FIG. 9, the adhesive 8 fed in an excessiveamount deposits and solidifies on the surface of the base wall 3h andsolidifies while dropping from the tip of the support portion 3d. As aresult, the contraction force of the adhesive 8 derived from hardeningand acting in the optical axis direction (direction z) is directlyexerted on the lens 4 and dislocates it.

As shown in FIG. 9, the contraction force of the adhesive 8 acting onthe base wall 3h, as mentioned above, is extremely strong because itacts on the lens surface of the collimator lens 4 directly andperpendicularly thereto. By contrast, the adhesive 8 solidified at thetip of the support portion 3d drops from the tip and does not directlycontact the lens surface. Therefore, the force of this part of theadhesive 8 is not critical. In light of this the non-adhesion portion G2terminating at the tip of the lens support portion 3d may be omitted,depending on the accuracy required of the light source device.

Referring again to FIGS. 3 and 4, the aperture forming member 5 has anaperture 5a and two pairs of lugs 5b and 5c for affixing the member 5 tothe base 3. On the other hand, the base 3 has two pars of arcuatepositioning grooves 3f and 3g. After the collimator lens 4 has beenfixed in place by the previously stated procedure, the aperture formingmember 5 is positioned such that its lug pairs 5b and 5c respectivelyface the groove pairs 3f and 3g of the stepped portion 3h of the base 3.Then, the member 5 is pushed toward the base 3. As a result, the lugpairs 5b and 5c respectively mate with the groove pairs 3f and 3g,affixing the member 5 to the base 3.

Two slots 3i are formed at the right and left end portions of the base 3and used to mount the light source device to a digital copier, laserprinter or similar image forming apparatus. At this instant, thevertical surface or front 3j of the base and the outer circumferentialsurface of the stepped portion 3h are used as a reference forpositioning.

FIGS. 10-13 each shows another specific configuration of thenon-adhesion portions G1 and G2. The configuration shown in FIG. 10lacks the annular recess 3 k and simply increases the distance betweenthe surface of the stepped portion 3h and the collimator lens 4 and thedistance between the tip of the lens support portion 3d and the lens 4.This is the simplest configuration.

The configuration shown in FIG. 11 is a modification of theconfiguration of FIG. 10. As shown, an upright wall 3m extends from thetip of the surface 3e of the support portion 3d. The wall 3m surelyprevents the excessing portion of the adhesive 8 from spreading over thetip of the support portion 3d.

In FIG. 12, a table portion 3n having a width substantially identicalwith the thickness of the lens 4 is formed on the surface 3e of thesupport portion 3d. The lens 4 is adhered to the table portion 3n. Inthis configuration, the excessive part of the adhesive 8 is received instepped portions located at both sides of the table 3n. Therefore, evenwhen the adhesive 8 is fed in an excessive amount, its contraction forcedoes not directly act on the lens surface so long as the the adhesive 8received in the stepped portions does not rise above the lower edge ofthe lens 4.

The configuration shown in FIG. 13 is a modification of theconfiguration of FIG. 12. As shown, the table portion 3n shown in FIG,12 is combined with the upright wall 3m shown in FIG. 11. This alsoprevents the adhesive 8 from spreading over the tip of the supportportion 3d.

While the adhesive 8 of the illustrative embodiment is ultraviolet lightcurable adhesive, it is only illustrative and may be replaced with anyother adhesive so long as it is photo-curable.

The embodiment described above has the following advantages.

(1) Because a collimator lens is directly affixed to a lens supportportion formed integrally with a base, a light source device needs aminimum number of parts and is low cost. Further, the device does notinclude any portion to be fastened by screws and therefore frees itsstructural parts from displacement due to fastening, thereby achievinghigh accuracy.

(2) The device allows the collimator lens to be fixed in place byphoto-curable adhesive despite that it prevents light issuing from asemiconductor laser from leaking in directions other than the opticalaxis direction.

(3) The collimator lens is adhered to the lens support portion having anarcuate shape by the photo-curable adhesive. This allows setting lightto be radiated toward the adhesive layer from above the lens, therebysetting the adhesive. Because the support portion and the optical axisof the laser are coaxial, the adhesive layer formed between the supportportion and the lens has a uniform thickness and solidifies evenly.Therefore, the device prevents the lens from being dislocated due to thecontraction of the adhesive in the event of hardening.

(4) Because the adhesive layer contacts only the lower half of the outercircumference of the lens, the contraction has directivity. It istherefore possible to provide the initial position of the lens with anoffset, taking account of a certain degree of contraction. This enhancesthe positional accuracy of the lens after it has been fixed in place.Because the setting or curing light can be easily radiated from abovethe lens, the irregular hardening is further obviated, and thepositional accuracy is further enhanced.

(5) Strains due to the contraction and acting in the right-and-leftdirection (direction x) are symmetrical and cancel each other. Thislimits the contraction only to the up-and-down direction (direction y)and thereby further improves the directivity of the contraction.Consequently, the device can be adjusted more accurately.

(6) A non-adhesion portion intervenes between the wall of the base andthe lens. Even when the adhesive is fed in an excessive amount, thenon-adhesion portion prevents it from directly depositing on the wall ofthe base; otherwise, the excessive developer would deposit and solidifyon the wall of the base and exert an intense contraction force on thelens in the optical axis direction (direction z). This enhances accuratepositioning in the optical axis direction.

(7) Another non-adhesion portion intervenes between the lens and the tipof the lens support portion. This non-adhesion portion prevents theadhesive from spreading as far as the tip of the support portion andsolidifying there. This further enhances accurate positioning in theoptical axis direction.

(8) The base for mounting the laser and lens thereon is formed ofinsulating resin having a coefficient of linear expansion of 2.3×10⁻⁵ /Kor below in the optical axis direction, and a thermal conductivity of0.9 W/m-K or above. Therefore, despite that the laser generates heat,the temperature of the device rises only slightly above the temperatureinside the body of an image forming apparatus. Moreover, such atemperature elevation does not cause the relative position of the laserand lens to change noticeably. Consequently, a stable collimationcharacteristic is maintained against changes in temperature.

(9) Because the base itself is insulative, a case surrounding the laseris fully electrically insulated without resorting to any specialinsulating structure. The device is therefore simple and low cost.

2nd Embodiment

Referring to FIG. 14, an alternative embodiment of the present inventionwill be described. As shown, the light source device has a base orsupport member 15 formed with a stepped through bore 16 substantially atits center. A semiconductor laser 12 is press fitted in the bore 16. Thebase 15 is formed of a substance opaque to infrared rays (about 780 nm)and light having shorter wavelengths. The base 15 has on its outersurface a first cylindrical surface 18 and a second cylindrical surface17 smaller in diameter than the first cylindrical surface 18. A guidepin 11 protruding from the right end of the base 15, as viewed in FIG.14, is passed through a positioning hole 10a formed in a printed circuitboard 10, and then affixed to the circuit board 10 by thermaldeformation. The laser 12 and circuit board 10 are electricallyconnected together by leads 12a.

A collimator lens 19 is formed of a material transparent to ultravioletrays. While the lens 19 may be implemented as a plastic lens or a glasslens, a glass lens is superior to a plastic lens as to opticalcharacteristic. The lens 19 has at its right end, as viewed in FIG. 14,a recess 20 for forming a clearance of about 0.5 mm (at each side)between the lens 19 and the smaller diameter cylindrical surface 17. Inthis condition, when the cylindrical surface 17 is loosely fitted in therecess 20, the clearance allows the lens 19 to be adjusted in thedirections x and y.

A method and a structure for supporting the collimator lens 19 on thebase 15 are as follows. The lens 19 is held by a chuck, not shown,movable in the directions x, y and z, and then finely adjusted in theabove three directions with the optical characteristic of the laser beambeing monitored. After the lens 19 has been fully positioned, anultraviolet radiator 22 radiates ultraviolet rays toward the assembly.Adhesive 21 is filled in the clearance between the cylindrical surface17 and the lens 19 either entirely or at a plurality of positions. Theultraviolet rays cause the adhesive 21 to solidify in a short period oftime. As a result, the lens 19 is affixed to the base 15. Of course, thethickness of the adhesive or adhesive layer 21 depends on the lightsource device. An aperture fang member 14 having an aperture 14a ispress fitted on the cylindrical surface 18.

3rd Embodiment

FIGS. 15 and 16 show another alternative embodiment of the presentinvention. In FIGS. 15 and 16, structural elements identical with theelements shown in FIG. 14 are designated by identical referencenumerals. As shown, the Light source device has a base or support member23 formed of the same material as the base 15, FIG. 14. Thesemiconductor laser 12 is press fitted in the through bore 16 formed inthe base 23. The guide pin 11 protruding from the right end of the base23 is received in the hole 10a of the printed circuit board 10 and thendeformed by heat. As a result, the circuit board 10 is affixed to thebase 23. The aperture forming member 14 is press fitted on thecylindrical surface 18 of the base 23. The configuration described sofar is identical with the configuration shown in FIG. 14.

In this embodiment, the smaller diameter cylindrical surface 17 isreplaced with a recessed surface 24 contiguous with the greater diametercylindrical surface 18. A cylindrical collimator lens 25 has an outercircumferential surface substantially parallel to the recessed surface24. When the lens 25 is held by a chuck, not shown, movable in thedirections x, y and z, a clearance of about 0.5 mm is formed between thelens 25 and the recessed surface 24.

The lens 25 is formed of the same material as the lens 19 of de secondembodiment. The lens 25 is finely adjusted in the directions x, y and zwith the optical characteristic of the laser beam being monitored.Subsequently, the adhesive 21 is filled in the clearance between thelens 25 and the surface 24. The ultraviolet radiator 22 radiatesultraviolet rays toward the assembly in order to cause the adhesive 21to solidify in a short period of time. As a result the lens 25 isaffixed to the base 23 by the adhesive 21.

As stated above, the second and third embodiments described above havethe following advantages.

(1) Because a collimator lens is adjustable in three differentdirections x, y and z), a single adjusting portion suffices This reducesthe number of structural parts of the light source device.

(2) Because a substantial clearance is available between the lens and asupport member, the accuracy required of the individual part is eased.Hence, the light source device is low cost.

(3) The decrease in the number of parts obviates portions to be fastenedby screws. This frees the parts from dislocation ascribable to fasteningan d enhances the accuracy of the device.

(4) Adhesive is hardened by ultraviolet rays transmitted through thelens. Hence, despite the structure preventing a laser beam from leakingin directions other than the optical axis direction, it is possible toilluminate the adhesive uniformly and cause it to fully harden. Thisobviates changes in the adhesive due to aging and frees it fromirregular hardening and unhardened portions.

4th Embodiment

Referring to FIGS. 17 and 18, a further alternative embodiment of thepresent invention will be described. As shown, the light source devicehas a semiconductor laser 33 for emitting laser light, a collimator lens39 for collimating the laser light to output a substantially parallelbeam, and a base or support member 35 supporting the laser 33 The base35 is formed of a material opaque to light having wavelengths shorterthan about 780 mm (infrared rays) inclusive.

The laser 33 is press fitted in a stepped through bore 35a formed insubstantially the center of the base 35. A pair of spacers 35b areformed integrally with the base 35. Guide pins 35c each protrudes fromthe respective spacer 35b. A printed circuit board 30 is formed withpositioning holes 30a slightly smaller in diameter than the guide pins35c. The base 35 is affixed to the circuit board 30 with its guide pins35 received in the positioning holes 30a. After the base 35 has beenaffixed to the circuit board 30, leads 33a extending out from the laser33 are respectively passed through holes 30b formed in the circuit board30. Then, the leads 33a are soldered to a conductive wiring patternprovided on the rear of the circuit board 30.

An aperture forming member 36 for forming an aperture 36a is partly cutand bent to form an elastic tongue 36b. The aperture forming member 36is received in a groove 35d formed in the base 35 and is fixed in placedue to the elasticity of the tongue 36b. The base 35 has a recessedsurface 35e. A collimator lens 38 has a contour substantially parallelto the recessed surface 35e. The lens 38 is held by a chuck, not shown,adjustable in position in the directions x, y and z. A clearance ofabout 0.5 mm is formed between the collimator lens 38 and the surface35e and filled with adhesive 31.

The collimator lens 38 is formed of a material transparent toultraviolet rays. While the lens 38 may be implemented as a plastic lensor a glass lens, a glass lens is superior to a plastic lens in respectof optical characteristic. After the aperture forming member 36 has beenaffixed to the lens 38, it is finely adjusted in the directions x, y andz while the optical characteristic of the laser beam issuing via theaperture 36a is monitored. Then, the adhesive is filled in the clearancebetween the lens 38 and the surface 35e of the base 35. Subsequently, anultraviolet radiator 32 radiates ultraviolet rays toward the assembly inorder to cause the adhesive 31 to solidify in a short period of time.Because the lens 38 is transparent to ultraviolet rays, the adhesive 31solidifies evenly and adheres the lens 38 to the base 35 whilemaintaining its collimation characteristic.

Assume that the above light source device is mounted to the body of adigital copier, laser printer or similar image forming apparatus or to ahost unit. The base 35 is generally L-shaped and has a first referencesurface 35f parallel to the optical axis, and a second reference surface35g perpendicular to the optical axis. To mount the device to theapparatus body or the host unit from above the apparatus body, thedevice is positioned in the direction of rotation (directions x and y)by use of two positioning holes 35h. Then, screws are driven into twothreaded holes 35i from above the device in order to fasten the deviceto the apparatus body with the first reference surface 35f contactingthe reference surface of the apparatus body. To mount the device to theapparatus body from one side of the apparatus body, the device ispositioned in the direction of rotation (directions x and y) by use oftwo positioning holes 35j and then fastened to the side of the apparatusbody via two threaded holes 35k. In this case, the second referencesurface 35g contacts the reference surface of the apparatus body.

The light source device may be assembled and adjusted by an automaticmachine by the following procedure. First, the base 35 is positionedsuch that its second reference surface 35g extends horizontally. Then,the leads 33a of the laser 33 are soldered to the conductive wiringpattern of the circuit board 30 from above the circuit board 30. Theoptical characteristic of the device is adjusted with the firstreference surface 35f held in a horizontal position. The steps ofinserting the aperture forming member 36, applying the adhesive 31,positioning the collimator lens 38, radiating ultraviolet rays are alleffected from above the device, so that the automatic assembly isfacilitated.

Of course, the first and second reference surfaces 35f and 35g may eachbe implemented by a respective support member. The aperture formingmember 36 and collimator lens 38 may be affixed to a single member, oreach may be affixed to a respective member. The member or members towhich the member 36 is affixed may be formed integrally with orseparately from the base 35. Even when the surface where the lens 38 islocated is different from the horizontal reference surface, it does noteffect the collimation characteristic of the lens 38 because the lens 38is affixed to the base 35 after the optical characteristics of the lens38 including the collimation characteristic have been examined.

The fourth embodiment described above has the following advantages.

(1) The light source device has a first and a second reference surfacerespectively perpendicular and parallel to the optical axis of asemiconductor laser. A collimator lens is fixed in place with itsoptical axis aligned with that of the laser. Hence, the device can bereadily mounted to an apparatus body or host unit without having itscollimation characteristic deteriorated.

(2) Because a base is implemented as a single molding, the device needsa minimum number of parts and is therefore low cost.

(3) The decrease in the number of parts obviates portions to be fastenedby screws. This eliminates the dislocation of the individual partascribable to fastening using screws and thereby provides the devicewith high accuracy.

(4) Ultraviolet light curable adhesive is solidified by ultraviolet raystransmitted through the lens. It is therefore possible to fully hardenthe adhesive by uniform radiation, and therefore to obviate irregularhardening and unhardened portions.

(5) Light issuing from the laser does not leak in directions other thanthe optical axis direction, so that the adhesive is free from variationascribable to aging.

(6) The focus of the lens can be adjusted after an aperture formingmember has been mounted. This prevents the optical characteristic frombeing varied after the mounting of the aperture forming member.

(7) Because the device has the first and second reference surfacesrespectively perpendicular and parallel to the optical axis of thelaser, it can be mounted to an apparatus body or host unit from above orfrom one side of the apparatus body, as desired. This provides thedevice with general-purpose applicability.

(8) The first reference surface allows the mounting of the apertureforming member, the application of the adhesive, the positioning of thelens and the radiation of ultraviolet rays to be effected from above thedevice without exception. These facilitate the automatic assembly andadjustment of the device.

Various modifications will become possible for those skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

What is claimed is:
 1. A light source device comprising:a flat basemember having a through bore; a semiconductor laser mounted on a rear ofsaid base member and fitted in said through bore, and for emitting laserlight; a lens mounted on a front of said base member at a front of saidthrough bore and coaxial with an optical axis of said semiconductorlaser; and a lens support member positioned at the front of said throughbore coaxially with the optical axis of said semiconductor laser, andhaving an arcuate section, and having a diameter slightly greater thanan outside diameter of said lens; wherein said lens is affixed to saidlens support member by photo-curable adhesive.
 2. A light source deviceas claimed in claim 1, wherein said lens support member is formedintegrally with said base member.
 3. A light source device as claimed inclaim 1, wherein said lens support member has an arc smaller than asemicircle.
 4. A light source as claimed in claim 1, wherein said lenssupport member has an arc symmetrical in a right-and-left direction. 5.A light source device as claimed in claim 1, further comprising anaperture forming member for shaping the laser light output from saidlens.
 6. A light source device as claimed in claim 1, wherein said lenscomprises a collimator lens.
 7. A light source device as claimed inclaim 1, wherein a non-adhesion portion is formed at least between saidlens affixed to said lens support member and a wall of said base member.8. A light source device as claimed in claim 7, wherein saidnon-adhesion portion comprises an annular recess formed in said wall ofsaid base member concentrically with said through bore.
 9. A lightsource device as claimed in claim 7, wherein said non-adhesion portioncomprises a groove having a width greater than a thickness of said lens.10. A light source device as claimed in claim 7, wherein saidnon-adhesion portion comprises a table portion having a lengthsubstantially identical with a thickness of said lens.
 11. A lightsource device as claimed in claim 7, wherein another non-adhesionportion is formed between said lens and a tip of said lens supportmember.
 12. A light source device as claimed in claim 1, wherein saidbase member comprises insulating resin having a coefficient of linearexpansion of less than 2.3×10⁻⁵ /K inclusive in a direction of theoptical axis, and a thermal conductivity of greater than 0.9 W/m.Kinclusive.
 13. A light source device comprising:a laser for issuing alaser beam; a lens; a base member having a through bore holding saidlaser; a support portion in a form of a projection formed integrallywith said base member and located downstream of said base member in adirection in which the laser beam advances in said through bore, saidsupport portion including a a surface extending in said direction; andadhesive filling a clearance between said surface of said supportportion and said lens positioned in directions of three axes; andwherein said laser is positioned such that the laser beam is propagatedthrough said through bore.
 14. A light source device as claimed in claim13, wherein said base member is formed of a material opaque to lighthaving a wavelength shorter than a wavelength of infrared rays (about780 nm) inclusive and wherein said lens is formed of a materialtransparent to ultraviolet rays.
 15. A light source device as claimed inclaim 13, wherein said adhesive filling said clearance forms a layersubstantially parallel to an optical axis.
 16. A light source device asclaimed in claim 13, further comprising a printed circuit boardelectrically connected to said semiconductor laser and affixed to saidbase member.
 17. A light source device as claimed in claim 13, furthercomprising an aperture forming member formed with an aperture forshaping the laser light output from said lens, and mounted on said basemember.
 18. A light source device as claimed in claim 13, wherein saidlens comprises a collimator lens.
 19. A light source device comprising:asemiconductor laser for emitting laser light; a first support membersupporting said semiconductor laser; a lens positioned coaxially with anoptical axis of said semiconductor laser; and a second support membersupporting said lens; wherein said first support member has a firstreference surface perpendicular to the optical axis of saidsemiconductor laser, wherein said second support member has a secondreference surface parallel to the optical axis of said semiconductorlaser, and wherein said first reference surface of said first supportposition and said second reference surface of said second supportportion are configured in an L-shape.
 20. A light source device asclaimed in claim 19, wherein said first and second support members areformed integrally with each other.
 21. A light source device as claimedin claim 19, further comprising an aperture forming member having anaperture for shaping the laser light issuing from said semiconductorlaser.
 22. A light source device comprising:a semiconductor laser foremitting laser light; a first support member supporting saidsemiconductor laser, wherein said first support member has a firstsurface formed with a through bore for mounting said semiconductor laserand a second surface parallel to an optical axis and positioneddownstream of said through bore in a direction of propagation of saidsemiconductor laser, wherein said first and second surfaces areconfigured in an L-shape, and wherein said first support member has abottom substantially parallel to said second surface and contacting amounting surface of a host unit; a lens positioned coaxially with anoptical axis of said semiconductor laser, wherein said lens is affixedto said second surface by an adhesive; a second support membersupporting said lens; an aperture forming member having an aperture forshaping the laser light issuing from said semiconductor laser; and athird support member supporting said aperture forming member on saidsecond support member from below said second support member; whereinsaid first support member is positioned perpendicularly to the opticalaxis, and wherein said second support member is located in front of saidfirst support member.
 23. A light source device as claimed in claim 22,wherein a surface for supporting said lens comprises a recessed surface.24. A light source device as claimed in claim 22, wherein a recess isformed in said second surface at a position downstream of said lens insaid direction of propagation of said semiconductor laser and whereinsaid aperture is received in said recess.
 25. A light source device asclaimed in claim 22, wherein said first, second and third supportmembers are formed integrally with each other.
 26. A light source deviceas claimed in claim 1, wherein said base member is formed of a materialopaque to light having a wavelength shorter than a wavelength ofinfrared rays (about 780 nm) inclusive, and wherein said lens is formedof a material transparent to ultraviolet rays.
 27. A light source deviceas claimed in claim 24, wherein said aperture forming member iselastically supported by said third support member.
 28. A light sourcedevice comprising:a base member having a through bore substantially at acenter thereof, a semiconductor laser fitted in said through bore andfor emitting a laser beam; and a lens mounted on a surface of said basemember; and wherein said lens is supported on said base member by a lenssupport member and said lens is positioned in directions of three axeswith adhesive filling a clearance between said lens and said surface ofsaid base member, wherein said lens support member is positioneddownstream of said through bore in a direction of propagation of saidlaser beam, and wherein a surface of said base member perpendicular tosaid optical axis is located at a downstream side of said base memberand contacts a host unit.
 29. A light source device as claimed in claim28, wherein a groove for mounting an aperture is formed on said surfaceof said base member perpendicular to said optical axis, and wherein saidaperture is fitted in said groove.